Using Ca-doped carbon dots as catalyst to amplify signal to determine ultratrace thrombin by free-label aptamer-SERS method.

The highly catalytic Ca-doped carbon dots (CDCa) were prepared by microwave procedure, that exhibit strong catalytic effect on HAuCl4-glucose (GLC) reaction to form gold nanoparticles (AuNPs) with high SERS activity, using Victoria blue B (VBB) as a molecular probe. The SERS intensity at 1615 cm-1 increased linearly with CDCa increasing, due to formation of more AuNPs nanosol substrate as indicator. When thrombin aptamer (Apt) was added in this system, Apt adsorbed on the CDCa surface to inhibit theirs catalytic activity, and the SERS intensity decreased. However, when thrombin (TB) was present, it can bind to Apt to form stable G-duplex of Apt-TB and free CDCa catalyst in the system, and the SERS signal increased linearly. Thus a free-label Apt-SERS quantitative analysis method was developed for ultratrace TB, with a linear range of 0.0058-0.115 nmol/L and a detection limit of 0.0018 nmol/L TB.